The present invention is related to a process of treating the juice of squeezed vegetable material, especially lucerne, various leguminous plants and pulps, used as fodder, with a view to producing alimentary proteins and super-nitrogenated protein food. The invention is also related to the products obtained by carrying out the above-mentioned process.
For about twenty years, it has been current practice to dehydrate various agricultural products adapted to be used as fodder (such as pulps, lucerne and various leguminous plants), by means of various industrial processes which all were based on directly drying the fodder in an oven, and more particularly in a rotary oven. These installations consume a considerable amount of fuel (about 0.3 ton per ton of final product) and involve high thermal or calorific losses. On account of the recent increase of the cost of petrol-based products, these conventional installations are no longer advantageous from the economical point of view. Recently developed processes endeavour to improve the rentability of dehydration by providing a supplementary treatment stage comprising squeezing of the vegetable matter, so as to reduce the amount of water to be eliminated in the oven. This allows the cost of dehydration to be considerably reduced, however such process involves the production of important amounts of squeezing juice (for example about 500 kg per ton fresh lucerne), resulting in losses of proteins and sugars, which are extracted from the squeezed vegetable matter together with the juice.
In the present description and in the claims by "squeezing juice" is meant "any juice resulting from the squeezing of vegetable material". Furthermore, by "medium" is meant the corresponding "culture medium" or "treatment medium".
Various methods have been disclosed for recovering the proteins from such squeezing juice, especially by thermo-coagulation by means of calories recovered from the dehyration oven.
These known processes allow about 50% of the energy to be recovered, as regards the operating cost. However these processes involve considerable investment, as they comprise complex operations that complicate to an important degree the carrying out of such processes in practice. Furthermore the standardization of the specifications concerning the recovered proteins stemming from the treated squeezing juice raises difficult problems.
Also, the above-mentioned known processes involve the requirement of perfectly controlling the squeezing conditions; it was found, in particular, that the squeezing of the vegetable matter must not be carried too far when it was desired to achieve a satisfactory recovery of the proteins carried off by the juice. More particularly it was found that it was necessary to produce a residual cake having a dry matter content of not more than 12% to 15%, with a view to achieving a satisfactory global balance. According to present knowledge it appears that when the vegetable matter is submitted to supersqueezing, so as to produce cakes having a dry matter content of up to 30 to 35%, such cake, as squeezed, have a comparatively low protein content which leads, in the final treatment stage, to producing pellets, the composition of which differs from the composition of the pellets obtained when conventional dehydration methods are applied. Furthermore it becomes increasingly difficult to recover by thermocoagulation the increasing amounts of proteins carried along by the juice. The energetic gain resulting from dehydration by supersqueezing thus is at least partly counterbalanced by quality loss and by a poor global balance of the recovered substances. It should be noted, too, that the supersqueezing method, while being advantageous as regards the energy consumption and cost involved in dehydrating the squeezing cake, leads to producing important amounts of juice (75,000 m.sup.3 juice in an average size unit of a capacity of 40 tons/hour treating 150,000 tons lucerne per campaign). The juice resulting from supersqueezing contains, amongst other constituents, a high amount of organic substances (especially proteins and sugars), so that such juice cannot be rejected directly into a river, on account of its elevated BOD value. It is thus necessary to be able to recover these organic substances prior to discarding the juice in the form of waste material. The thermocoagulation treatment allows only part of these substances (coagulable proteins) to be recovered. Furthermore, on account of the high volumes involved, the juice thus produced must be stocked in important quantities; however these juices are most unstable and highly fermentable. It is thus necessary to be able to stabilize the same, either by refrigeration (which is very expensive) or by adding bacteriostatic and fungiostatic agents, which is also a most expensive method, raising furthermore complex problems as regards consecutive toxicity risks of the thus recovered products. Consequently these approaches are not acceptable from an economical point of view.
The present invention has for its main object to provide a process for treating squeeze juice obtained by squeezing vegetable fodder material, which allows the following advantageous effects to be obtained:
(1) stabilizing the juice (thus avoiding undesirable fermentation phenomena),
(2) insolubilizing the proteins (i.e. render said proteins insoluble),
(3) increasing the protein content by producing a biomass which can be consumed by animals,
(4) obtaining by-products constituted by mineral compounds having a high nitrogen content which can be used as fertilizers and as alimentary (or nutritive) additives,
(5) producing a residual effluent which can be rejected into a river and the BOD and COD values of which are acceptable for the natural environment.
The process of treating squeezing juice according to the present invention comprises:
submitting the juice issuing from a squeezing press to a first inoculation with a first mixture of mesophile homofermentative lactic bacteria in an amount of at least 10.sup.4 bacteria per milliliter;
maintaining the thus inoculated juice at a temperature of 28.degree. to 35.degree. C., preferably 30.degree. C., during 15 to 20 hours, under slow stirring and without aerating, so as to obtain a suspension constituted by an insoluble fraction of vegetable proteins and microbial proteins, and a residual liquid phase, said suspension having a pH of 4.2 to 4.5;
separating said insoluble fraction from said liquid phase; and
treating separately the residual liquid and said insoluble phase.
In one embodiment of the process according to the invention, the suspension is submitted, prior to the step of separating said insoluble fraction from said liquid phase, to a second inoculation using a second mixture of thermophile homofermentative lactic bacteria in an amount of 10.sup.4 germs per milliliter per 10 cubic meters suspension, the thus inoculated suspension being maintained at a temperature of 40.degree. to 50.degree. C., preferably 45.degree. C., during 18 to 20 hours, the final suspension thus obtained having a pH of 3.3 to 3.6
Broadly speaking the process according to the invention is based on the rapid growth of lactic bacteria directly promoted by the sugars present in the heterogeneous media. Said process then allows lactic acid and/or ammonium lactate to be obtained by a succession of operating phases or stages involving an evolution of the pH of the medium, as will be described herein-below.